1. There are six series * * *, four of which are 1, and the other two are different, so there are * * * series satisfying the above conditions.

Solution: choose 4 out of 6 1, and the other two are arbitrarily arranged.

C(6，4)*A(2，2)=C(6，2)*2= 15*2=30

2. The solution of equation 3A8x=4A9(x- 1) is-(A is followed by subscript and then superscript, and so on).

Solution: 3*8! /(8-x)！ =4*9/( 10-x)！

3=36/(9-x)( 10-x)

(9-x)( 10-x)= 12=3*4

x=6

3. The solution set of inequality A(n- 1)2+n≤ 10 is ........

(n- 1)(n-2)+n≤ 10

n？ -2n+2≤ 10

n？ -2n-8≤0

(n-4)(n+2)≤0

-2≤n≤4

Because n- 1≥2, that is, n≥3.

So n=3, or n=4.

Solution set {3, 4}